Note: Descriptions are shown in the official language in which they were submitted.
26~
PROTECTOR llNIT FOR TEL.ECOMMUNICATIONS CIRCUITS
Background of the Invention
Field of the Invention
This invention relates to electrical protec~ive
devices. More particularly, it relates to devices for
protecting communications circuits against excessive
voltage surges and excessive currents.
Description of the Prior Art
In telephone engineering, it is usual practice to
provide protectors at central offices for each incoming
line. These protectorsl which may be termed units or
modules, combine protection against excessive voltages
resulting from lightning, for example, with protection
against sneak currents. Sneak currents are not strong
enough to do any damage if they flow briefly, but may
generate enough heat to char conductor insulation and do
other damage if allowed to persist. The sneak currents are
produced by voltages of relatively low magnitude as
compared to the excessive voltages mentioned hereinabove
and usually result from accidental interference between
telephone lines and adjacent power lines.
Protection o~ a telephone line against excessive
voltage is usually provided by a so-called spark~gap
protector which generally includes a pair of spaced carbon
electrodes or a gaseous discharge device. One of the
electrodes is usually connected to ground, and the other is
usually connected to the incoming telephone line. Should a
high voltage be impressed on the line, it will bridge the
space or gap between the electrodes and cause current to
flow to ground, thus bypassing sensitive equipment which is
associa~ed with the line.
The second type of protection is commonly
provided by a device that is referred to as a heat coil.
The heat coil includes a coil of small gauge~ high
resistance wire which is wound on a metal sleeve inside of
~ Z~26~
which a contact pin is held in a predetermined position by
a fusible bonding material such as solder, for example.
Should excessive currents occur on the line and persist,
sufficient heat will be generated by the coil of wire to
melt the solder and release the pin. A spring is usually
provided which urges the released pin into electrical
contact with a source of ground potential to ground the
line and protect sensitive line equipment.
A protector assembly of this general type is
disclosed in U.SO Patent No~ 2,546,824. A contact pin of a
heat coil subassembly protrudes into a bore that extends
through one of two carbon block electrodes of the spark gap
protector and is releasably held in a sleeve by a solder
joint. lt includes a pair of springs, one of which retains
the elements of the assembly in abutting relation. When
the pin is released by current build up in the heat coil
that melts the solder joint, the other spring urges the
contact pin through the one carbon electrode into
engagement with the other electrode which is connected ~o a
source of ground potential.
Inasmuch as a ring conductor and a tip conductor
are associated with each telephone station apparatus, each
telephone line requires two protector assemblies~ A
telephone circuit protector unity shown in U. S. Patent
No. 3,573,695, includes two protector assemblies enclosed
in a single insulative housing to save space, to protect
the assemblies from dust, and to facilitate installation.
Each protector assembly includes a spark~gap subassembly,
having spaced carbon blocks, for excessive voltages, and a
heat coil subassembly for excessive currents. The spark~
gap and heat coil subassemblies are held in abutting~
aligned relation by a single spring which is part of the
normal transmission circuit. The spring also serves to
propel a pin of the heat coil subassembly into engagement
with a grounding circùit, which includes one of the carbon
blocks, during the passage of excessive currents through
the heat coil. In this patent, the axis of each heat coil
pin is aligned axially with the axis of its associated
carbon blocks.
While units such as those described hereinabove
have proved very useful in protecting telephone circuits
5 from excessive voltages and currents, efforts have been
made to introduce improvements~ For example, to complete a
fault current path to ground, the pin in the heat coil
subassembly must be brought into contact with a carbon
block in the spark-gap protector subassemb~y~ This causes
excessive heating of the spark-gap subassembly which
becomes part of the fault path. Heat build up in the
carbon blocks of the spark-gap subassembly is commonplace
because of their relatively high resistance. A further
disadvantage is that the physical arrangement of the heat
coil subassembly utilizes excessive space within the
protector module. This, together with the extension of a
contact pin through the voltage protection portions of the
protector, has precluded the use of gaseous discharge
devices in place of carbon blocks. Gaseous discharge
^20 devices are desirable because of ~heir longer lives and
because they afford better control of the breakdown
voltage. Further, the need for recesses in the carbon
blocks prevents heat shielding of these elements. Because
the carbon blocks are provided with recesses, oftentimest
particles which become dislodged drop into and short the
spark gap. As a result, normal spark-gap-type operation
may be precluded.
These last mentioned problems have been overcome
by a protector unit shown in U.S. Patent No. 4,215,381
The unit includes a heat coil subassembly for sensing
excessive currents and a voltage surge limiter asse~bly
which is axially aligned with the heat coil subassembly for
conducting excessive voltages through a grounding
subassembly to ground.
In this arrangement, gaseous discharge devices
may be used inasmuch as the voltage protection portion of
7~
the protector is taken out of the fault circuit. When
sufficient heat is transferred to the heat coil subassembly
such as by a current fault, a fusible alloy melts to allow
a spring to cause a heat coil flange to move and touch a
laterally projecting tab of a ground terminal assembly.
This creates an electrical path external to the voltage
protector subassembly through to the ground terminal
assembly. If a prolonged voltage surge occurs, there is an
arcing over in the voltage surge limiter assembly, the
fusible alloy is melted, and the spring moves the heat coil
flange plate as before.
Al-though this protector unit overcomes the
problem of prior art arrangements, which precluded the u~e
of gaseous discharge devices for voltage surge protection~
it continues to use a spring as part of the normal and
fault current circuits. Since the spring moves slidably,
insulating sleeves are disposed about the spring to prevent
shorting. At times, the presence of the spring in the talk
circuit results in noise on the line.
~ protector unit in which the spring is not in
the talk circuit is disclosed in U.S. Patent No. 4,168,515.
That unit includes two heat coil subassemblies which are,
together with the line pins, individually mounted on
dielectric sub-bases. Both sub-bases are supported by a
separate main base structure of the protector. The ends of
the heat coil are welded to conductive plates to which the
line pins are staked r the windings of the coil being
directly in the line circuitO During over~current
conditions, a fusible alloy is melted by the heat coil
causing a conductive cup to move into engagement with a
conductive plate that is connected to a line pin, thereby
forming a direct metallic shunt to ground. In order,
however, for the protector components to fit within a
standard-sized housing, which is necessary for
interchangeability with other protector units~ a thin main
base supports the two sub bases. Such a thin base provides
less support for the line pins~ Furthermore, the local
~z~
side stresses imparted on the holes within the main base
may result in their permanent deformation and pin
misalignment.
A relatively simple protector device having a
minimum number of components, and in which there is no
spring in the talk circ~1it, is the subject matter of
Canadian Patent application, Serial No. 427,896, filed
on May 11, 1983, invented bv J. L. Cha~man,
P. S. Nelson~ and T. A. LaValle. In this protector
assembly, current protection is effected by a heat coil
subassembly which includes a sleeve disposed concentrically
about an extension of the line pin through the supporting
dielectric protector base. This sleeve is releasably
secured to the line pin by a fusible bonding material and
has convolutions of wire wrapped thereabout. One end of
the resistance wire is welded to one end of the sleeve,
which engages a vol*age protection subassembly. The other
end of the wire is welded to the central office pin mounted
through the base.
In manufacturing protector assemblies of this
type, the convolutions of wire cannot be wound around the
heat coil sleeve prior to being disposed on the line pin.
Since one end of the wire must be welded to the central
office pin on ~he base, a free end of wire would have to be
left on a prewound sleeve, which would be difficult to
mechanically locate for welding to the pin. Furthermore, a
nonfixed wire wrapped sleeve would tend to unwind, leaving
air gaps, which would change the heat transfer to the
sleeve. Accordingly, mechanical assembly is best efected
by affixing one end of the wire to the sleeve, winding the
wire thereon, and affixing the other end of the wire to the
central office pin. Difficulty arises, however, in
automechanically implementing such procedure for
manufacturing a protector unit which includes the standard
two protector assemblies necessary for individually
protecting the tip-and~ring conductors of a telephone
circuit. Because of the close proximity of the two heat
~Z~?2~0
-- 6 --
coil s]eeves, the machine operations of welding and wlre-
wrapping would be extremely cumbersome.
Summary of the Invention
The foregoing problems have been overcome by the
protector unit of this invention. The protector unit
includes a dielectric housing for supporting two protector
assemblies and a grounding subassembly that is attached to
connect each assembly to a source of ground potential when
excessive voltage increases and excessive current increases
appear in a circuit having two conductors such as the tip~
and-ring conductors of a telephone circuit. Two voltage
protection subassemblies are electrically connected to the
groundiny subassembly for conducting current associated
with excessive voltage surges on either conductor to ground
potential. Two heat coil subassemblies divert excessive
current increases on either conductor to the grounding
subassembly. Each heat coil subassembly is mounted on a
half-base which also supports an input and output pair of
conductive elements associated with one of the conductors
The two half~bases are held in mated position theretogether
by the dielectric housing. Each heat coil subassembly
includes a sleeve having resistance wire wrapped thereabout
which is directly in series with the input and output
conductive elements on the half~base. In the preferred
embodiment of the invention, the sleevè of each heat coil
subassembly is disposed concentrically about the input
conductive element on its associated base half and
releasably secured thereto by a fusible bonding material.
One end of the resistance wire is bonded to one end of the
sleeve~ and the other end of the wire is bonded to the
output conductive element on the base half. Voltage
protection subassemblies are held in engagement with the
heat coils by springs interposed between the voltage
protection subassemblies and the dielectric housing. When
the current flow through the resistance wire of either heat
coil is above a predetermined level, sufficient heat is
transferred to the sleeve to melt the fusible bonding
7~
material This permits the spring to cause the sleeve to
move along the input conductive element to engage the
grounding subassembly and provide a current path from the
, input conductive element to the source of ground potential.
In the protector unit of this invention, the heat
coils are directly in series wi~h the current flow in each
conductor of the protected circuit, and the springs are
removed from these current paths, thereby eliminating
potential sources of noise in the line. Advantageously, by
disposing the wire~wrapped sleeves of each heat coil assembly
on a separate half-base, the mechanical steps of winding the
. heat coils and bonding the ends of the resistance wire to
the conductive elements and ~he sleeve, can be readily
automechanized without the physical interference of an
adjacent heat coil subassembly.
In accordance with an aspect of the invention there
is provided an electrical protector unit for protecting a
circuit having first and second conductors against excessive
current increases and voltage surges, said protector assembly
comprises a dielectric housing for supporting the unit; a
grounding structure; a dielectric base structure; two input
and two output conductive elements arranged in pairs and
supported in said dielectric base structure; first and
second current responsive means for sensing said excessive
current increases in said first and second conductors,
respectively, and diverting said excessive current increases
to said ground structure, said first and second current-
responsive means being supported on said dielectric base
structure, each current-responsive means including a
resistance wire in direct electrical series with a pair of
associated input and output conductive elements; and means
for conducting voltage surges in either of said conductors
to said ground structure characterized in that said
dielectric base structure consists of a first base half and
a second base half, each base half supporting a pair of
~?Z~7~
- 7a -
input and output conductlve elements and one of said current
responsive means, said first and second base halves held in
mated position theretogether by said dielectric housing.
, Brief Description of the Drawing
Other features of the present invention will be
more readily understood from the following detailed
description of specific embodiments thereof when read in
conjunction with accompanying drawings, in which:
FIG. l is a perspective view of an arrangement for
mounting a plurality of electrical protective devices of ,
this invention;
FIGS. 2A and 2B are perspective views of a protector
unit of this invention;
FIG. 3 is an exploded perspective view of the
electrical protective device of this invention;
FIG. 4 is a front elevational view of the device of
FIG. 2;
FIG. 5 is a side elevational view of the device of
FIG. 2;
FIG. 6 is a plan view of the device shown in FIG. 4;
FIG. 7 is a front elevational view partially in
section of the device of FIG. 2;
FIG. 8 is a side elevational view of the device of
FIG. 2 partially in section;
~L2~2;7~
8 --
FIG. 9 is a front elevational view of a heat coil
subassembly and half~base of the protector unit of this
invention;
FIG. lO is a side elevational view of the heat
coil subassembly and half~base of FIG. 9;
FIG. ll is a plan view of a portion of the half-
base of the heat coil subassembly of FIG. 9;
FIG~ 12 is an elevational view of a central
office pin;
FIG. 13 is an elevational view of a pin~eyelet
assembly which comprises a portion of the heat coil
subassembly of FIG. 9;
FIGS. 14A and 14B are schematic views of a prior
art protector device and the protective device of this
invention;
FIG. 15 is a front elevational view of a ground
spring assembly of the device of FIG~ 2;
FIG. 16 is a side elevational view of a ground
spring assembly of FIG. 12;
FIG. 17 is a plan view of the ground spring
assembly of FIG. 15;
FIG. 18 is an exploded perspective view of an
alternative embodiment of this invention;
FIGS. 19-21 are elevational views and p]ans of
the alternate embodiment of the protective device of this
invention which includes facilities for engaging test
probes;
FIG. 22 is an elevational view of a portion of a
spring retainer;
FIG. 23 is a plan view of the retainer shown in
FIG. 22;
FIG. 24 is an elevational view of an insulator;
and
FIGS. 25-27 are views of a strap for use with the
embodiment shown in FIG. 18.
J
~2~
_ g _
Detailed Description
Referriny now to FIG. 1, there is shown a panel
which is designated generally by the numeral 20, and which
has a plurality of sockets 21-21 therein for receiving a
plurality of pins projecting from an array of circuit
protector units, designated generally by the
numerals 30-30. It should be apparen-t that since the
panels 20~20 are existing, the holes for receiving the pins
of protector units are established. Accordingly, any
protector unit which is to be used therewith must have its
terminal pins aligned with those holes.
Referring now to FIGS. 2-6 of the drawings, there
is illustrated a preferred embodiment of the protector unit
of this invention~ A plastic housing 32 is shown with a
base subassembly 34 which is snap-fastened thereto by
tangs 35-36 (see FIG. 2A~ on the base which are received in
two pairs of slots 37-37 in the housingO As can be seen in
the drawings, a finger grip 3B is provided adjacent to a
closed end of the housing.
As can be seen in FIGS. 3 and 7, a pair of
protector assemblies, designated generally by the
numerals 40 and 40' D are enclosed in the housing 32. One
of the protector assemblies provides protection for a ring
conductor, and the other provides protection for a tip
conductor of an associated telephone circuit (not shown).
But for base portions of each, the protector assemblies 40
and 40' are structurally identical to each other.
Therefore, but for the base portions of each, the same
numerals will be used for corresponding parts of the two
protector assemblies with the general designation of
subassemblies for one having a primed superscript.
Referring particularly to FIG. 3, it can be seen
that each protector assembly 40 includes a currenk overload
or protection subassembly which is designated generally by
the numeral 41, a voltage protection subassembly which is
designated generally by the numeral 42, and a compression
spring 43. The voltage protection subassembly 42 is
~2~
-- 10 --
sometimes referred to as a volta~e sur~e limiter
subassembly. The protector unit 30 also includes ~
grounding subassembly which is designated generally by the
numeral 44, and which is common to both assemblies 40
S and 40'.
The current protection subassembly 41 of the
protector assembly 40 includes a current responsive
portion 50 (see FIG. 3) which is generally referred to as a
heat coil subassembly. The heat coil subassembly 50 is
mounted in a left-hand base portion 51, as viewed in
FIG. 3, and the heat coil subassembly 50' is mounted in a
right-hand base portion 52. The left-hand and right-hand
portions 51 and 52, which together comprise the base 3~,
are mirror images of each other and, in a preferred
embodiment, each is made of a plastic insulating material
such as polybutylene terephthalate (PBT). Each base
half 51 and 52 (see FIGS. 9-11) also includes a semi-
cylindrical passageway 53 formed from a surface 54 to a
lower surface 56 thereof. This passageway 53 in one base
half is designed to cooperate wi-th the passageway in the
other base half when the two are mated together to form the
base subassembly 34.
Each portion of the base subassembly 34 supports
first and second electrical contact elements which form
part of the normal circuit current path. One of these is a
central o~fice pin 57 (see FIG. 12) which is mounted in an
interference fit in a bore 58 in each one of the base
portions. A headed portion 59 of each central office
pin 57 extends above the surface 54 of each base halE.
Each heat coil subassembly includes a pin-eyelet
subassembly (see FIG. 13). The input to each protector
assembly 40~40' of the protector unit 30 is through the
pin-eyelet 60 subassembly. The pin-eyelet subassembly 60
includes a line pin 61, which is received in an
interference fit in a bore 63 in the base half 51 (see
FIG. 9).
~Z~ 70
- 11 -
The pin~eyelet subassembly 60 also includes an
eyelet 62. The eyelet 62 has the configuration of a sleeve
or spool, and includes a central passageway 6~ and two
flanges 66 and 67, and is designed to hold a plurality of
convolutions of a resistance wire 69 thereon. The upper
flange prevents any jamming of the heat coil subassembly 50
oetween the voltage protection subassembly 42 and the
housing 32.
The eyelet 62 is secured in a Eirst position to
one end of the line pin 61 by means of a fusible bonding
material 70 (see FIGS. 7 and 13) such as solder, for
example, which has a predetermined ~elting point. The line
pin 61 of the pin-eyelet subassembly 60 also includes a
flange 71 and a rib 73, which are spaced between the lower
end of the line pin and the lower flange 67 of the eyelet.
The wire 69, which is wound about the hub of the
eyelet 62, is made from an alloy such as nichrome which, in
a preferred embodiment, is covered with nylon insulation
having a wall thickness of 0.008 cm~ In the preferred
embodiment, the wire 69 is such that its resistance between
the line pin 61 and the central office pin 57 is not
greater than 4 ohms. One end of the wire 69 is welded to a
hub 74 of the eyelet adjacent to an end 76, and an unwound
trailing end is welded to the head 59 of the central office
25 pin 57 (see FIG. 9)~ The eyelet 62 is made of a metallic
material, since it is a part of the loop circuit. The
wire 69 is insulated, since it is wound on the metallic
hub 74 of the eyelet wlth its convolutions generally
touching one another.
A normal circuit path for the current is from the
line pin 61 through the sleeve 62, through the wire 69 of
the protector assembly 30, and out through the central
office pin 57. When there is a current overload, the
circuit through the line pin 61 into the metal eyelet 62
and through the wire 69 to the central office pin 57 causes
the temperature of the wire to increase. The increased
temperature is sufficient to cause the fusible alloy that
~Zq~2~
- 12 -
bonds the eyelet hub 7~ to the pin 61 to melt and permit
relative movement between the eyelet and the pin.
It should be understood that while an eyelet is
used in the preferred embodiment, other equivalents could
be used. For example, an unflanged sleeve having a
passageway therethrough for receiving the line pin 61,
could be used. Moreover only the ends of the sleeve or
the eyelet need be conductive with one end of the insulated
resistance wire 69 being bonded to one end of the sleeve
and with the other end bonded to the headed end of the
central office pin 57.
Other arrangements within the scope of this
invention are also possible for the heat coil assemblyO
For example, an eyelet having conductive flanges and a
nonconductive hub could be used. The conductive flanges
would be bonded to the line pin 61 with the fusible alloy.
Uninsulated wire could be wound on the nonconductive hub
with the convolutions spaced apart with one end of the wire
bonded to a flange and the other linear trailing end welded
to the head of the central office pin as before. As the
temperature of wire increases, the hub~ which could be some
thermally conductive material, will transmit the heat
energy to the fusible alloy to melt it and allow operation
of the heat coil as before.
The pin-eyelet assembly 60 is mounted irl an
interference fit in the bore 63 of the heat coil base 51
~see FIGS. 9-11) such that the lower flange 67 of each
eyelet 62 is spaced above the top surface of the base.
Moreover, the flange 71 and the rib 73 of each line pin 61
are received within the base in order to cause the line pin
to be able to resist substantial forces which may be
applied axially thereof.
Advantageously, the rib 73 about each of the line
pins 61-61 causes an interference fit between the plastic
of the base half 51 and the pin which is able to resist the
force of about five pounds. Such a force may be generated
by plugging a protector unit 30 into the central office
~Zq?;2671;1
- 13 -
panel 20. Moreover, the shoulder 71, formed on each of the
line pins 61 hl, is adapted to resist the thrust imparted
to the pin assemblies generated b~y other portions of the
unit 30. The rib is required to resist the pushing thrust
which is in an opposite direction to that experienced by
the shoulder 73~
Unlike prior art protector assemblies, the line
pin 61 of the protector assembly 40 of this invention for a
conductor of each circuit forms a portion of the heat coil
portion 50 current pro~ection subassembly 41. This can be
seen best by comparing FIGS. 14A and 14B. In FIG. l~A is
depicted a prior art protector module which includes a heat
coil portion 75, a line pin subassembly 76~ and a ground
subassembly 77 ~ and the voltage protection subassembly 42 ~
15 As can be seen in FIG. 14A, the heat coil subassembly 75 is
aligned wlth the voltage protector subassembly 42~ but is
offset from the line pin 113~ In the protector assembly 40
of this invention (see FIG. 14B) ~ the line pin 61 is
aligned with the heat coil, but is offset from the voltage
20 protector subassembly 42~
When the right-hand and the left-hand base
assemblies 51 and 52r respectively, are mated together to
form the base 34 I the semi~cylindrical passageways 53~53
are brought together in order to form a cylindrical
25 passageway (see FIG. 7) for receiving a ground pir. 81 of
the grounding subassembly 44. The grounding subassembly 4
is shown in FIGS. 15-17 and includes the pin 81 having a
shoulder 84 which is riveted to a ground plate 86 which is
disposed along the top surface of the mated base halves 51
30 and 52~ When so disposed, portions of the ground plate 86
are received between the lower flange 67 of each one of the
pin eyelet assemblies 60-60 and the top surface 54 of the
half-bases 51 and 52 (see FIGS. 7-8)o The ground spring
plate 86 is disposed between the central office pin 57 and
35 the line pin 61 of each half of the base.
The ground pin 81 of the grounding subassembly
also includes a shoulder 87 (see FIGS 15 and 16). The
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- 14 -
shoulder 87 is surrounded by plastic of the base 34 when
the pin 81 is disposed within the passageway 53.
The grounding subassembly ~ also includes a
bifurcated portion 88 which extends upwardly from the
plate 86 and inwardly toward a centerline 89 of the ground
p;n 81 (see FIG. 16). As such, each one of upwardly
extending fingers, or furcations 91-91, is spaced to one
side of the centerline which extends through the ground
pin.
The fingers 91-91 are configured to establish
electrical contact with the voltage protection portion ~2
of the module 30O Referring to FIG. 8, it can be seen that
the free ends of the fingers 91-91 are shaped to bear
against an inner surface 92 of the housing 32 to insure
electrical contact with the voltage overprotection
device 42 (see FIG. 8)o One finger 91 enyages a metallic
cup 93 which houses the voltage protection subassembly 42
for the protection assembly 40, and the other finger 91
engages the cup 93 ~hich houses the voltage protection
subassembly 42 for the protector assembly 40'.
The voltage protection subassembly 42 of the
protector assembly 40 includes a surge limiter having a
pair oE electrodes, such as a pair of carbon blocks, for
example (see FIG 7). It should be understood that
although carbon blocks are shown in the drawings for the
voltage overprotection devices, gas tubes, which are well
known, also could be used. The cup 93 is positioned such
that a lower one of the carbon blocks, as shown in E`IG. 7,
has its electrode protruding therefrom to engage the upper
flange 66 of an associated one of the pin-eyelet
assemblies 60. The carbon blocks are received in the
cup 93 in a manner to space them apart through a
predetermined gap 99. The gap 99 is effective during a
voltage protection mode of the protector to cause a
sufficiently high voltage to bridge -the gap and cause
current to flow to ground~
~2~ 670
- 15 -
More particularly, the voltage protection
subassembly 42 comprises the cup 93, which supports the
center carbon electrode 101, or insert which is disposed
within a porcelain shell 103. The center carbon electrode
extends through an opening 104 in the porcelain shell and
protrudes therebeyond a distance of 0.13 cm. The other end
of the carbon electrode 101 is spaced a distance of
0.008 cm. from a plane through the open end of the
porcelain shell 103~ I'he carbon electrode 101 is bonded to
the walls of the opening in the porcelain block. Also
disposed within the cup 93, and in engagement with a closed
end thereof, is a carbon block 106 which is called a base
electrode. The base electrode 106 engages the annular rim
of the porcelain shell 103. This causes the base
15 electrode 106 to be spaced from the center electrode 101 a
distance of 0.008 cm. This gap, which is thereby
established between the center electrode 101 and the base
electrode 106~ is predetermined in accordance with the
level of voltage protection desiredO
When a surge of excessive voltage is generated in
a telephone line by a lightning strike, for example, the
resulting potential enters the current protector through
the ring conductor protected by protector assembly 40, the
tip conductor protected by the protector as~sembly 40'~ or
both conductors. Assuming that the potential enters
through the ring conductor, it bridges the associated
gap 99 between the center electrode 101 and the base
electrode 106 oE the protector assembly 40 and is conducted
to ground potential through the cup 93 and the ground
assembly 44 (see FIG. 14B).
As can be seen in FIGS. 3, 7, and 14B of the
drawings, an upper portion of each of the voltage
protection subassemblies 42-42 is engaged by a compression
spring 43 which also engages an inner portion 112 of the
housing 32 of the protector unit. The spring 43 maintains
the center electrode 101 in engagement with the eyelet 62.
Also~ the spring is adapted to cause the eyelet 62 to be
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- 16 -
moved from an initial, first posit;on on the llne pin 61
where it is bonded to the line pin to a second position
where a flange 67 of the eyelet engages the base plate 86
of the ground spring assembly 44.
It is significant that each of the line pins 61
comprises a portion of associated heat coil subassembly 50
(see FIGS. 9 and 14~) and is aligned vertically with the
eyelet 62 thereof. The centerline of the line pin 61 and
of the heat coil is offset 0.22 cm. from the centerline of
the voltage protection subassembly 42. This is unlike
prior art protector assemblies in which the heat coil
assembly is aligned with the centerline of the voltage
protectiOn subassembly 42 (see FIG. 14A). As a result, the
use of a separate line terminal assembly is obviated. The
line pin 61 and eyelet 62 with the winding, of the
resistance wire 69, are made in one assembly, thereby
reducing the number of parts for the protector assembly 30.
In accordance with the present invention, by
mounting a line pin 61, an eyelet 62, and a central office
pin 57 for each protector assembly 40 and 41 on separate
hal~-bases 51 and 52, respectively, the winding of
resistance wire 69 onto each eyelet 62 can be
automechanically implemented. Without the physical
interference of an adjacent pin and eyelet assembly, the
resistance wire 69 is automechanically welded to one end 76
of eyelet 62, wrapped thereabout, and welded -to central
office pin 57.
Another advantage of the protector assembly ~0 of
this invention is that the spring 43 is removed from both
the normal talk and fault current paths. It provides a
force for urging the eyelet 52 into engagement with the
ground plate 86, but is not in the normal current path or
the fault current circuit. The current 10w path for the
prior art protector module shown in FIG. 14A is up through
the pin 113 and terminal 76~ through a pressure contact
with a pin of the heat coil subassembly 75 and the heat
coil winding, through a pressure contact with one end of a
~Z~ ;70
- 17 -
spring 11~, such as in U.S. patent No. 4,215,381, through
the spring to another pressure contact with a bottom
plate 116, through a bottorn plate 116, and out through a
central office pin 117. For a voltac3e fault, the current
flows through the voltage protector 42 and out through the
ground terminal 77 and a ground pin 119. In the event of
current overload, the fusible alloy which bonds the heat
coil subassembly 75 to a pin is melted to allow the
spring 11~ to urge the heat coil flange into engagement
with a tab 118 that is connected to the ground pin 119.
Since the spring 114 moved, it was necessary to use
insulators to prevent a short circuit. Because the
spring 43 in the protector assembly 40 of this invention is
not in the circuit path, the insulating sleeves are not
requiredO
In the protector unit 30 of this invention, the
wire 69 which has convolutions wound on the eyelet 62 of
the pin-eyelet 60l functions as a resistance element with
the heat being concentrated therein. In a normal operating
mode, current flows in through the line pin 61, through the
convolutions of the wire 69 wound on the eyelet 62, and out
through the central office pin 57. Advantageously, all the
connections between these parts which constitute the
current path, are connected by welding or by soldering with
no pressure contacts as in prior ar~ protector assemblies.
In the event of excessive current, the current
path is as before, except that since the current exceeds
that of the design load, the unit overheats from the energy
generated by the excessive current. The wire 69 generates
heat which is transferred to the eyelet 62, and which is
sufficient to cause the fusible alloy which bonds the
eyelet to the line pin to melt. At that time, the
spring 43 becomes effective to move the eyelet 62 from its
first position where it is bonded to the pin 61 toward the
base to a second position where it engages the plate ~6 of
the ground plate assembly (see FIG. 14B). The lower
flange 67 of the eyelet 62 functions as a shunting element.
~2~ ;7~
18 -
As a result, the current flows through the line pin ~1, the
eyelet h2, and directly to the ground plate, substantially
shortening the current path frorn that of prior art
protector assemblies.
In the event of a voltaqe overload, the current
moves as before through the line pin 61, through the pin-
eyelet assembly 60, through the center electrode lOl of the
voltage protector bridging the gap 99, to the base
electrode 106, into the cup 93. There is a spark-over
between the center and the base electrodes 101 and 106,
respectively, o the voltage protector subassembly.
Current is conducted through the spring finger 96 to the
ground plate 86, and out the ground pin 81, to the source
of ground potential. In the event of a sustained voltage
surge, sufficient heat is transferred through the eyelet 62
to melt the alloy which holds the eyelet and line pin 61
together. At tha~ time, as before, with the excess current
occurrence, the eyelet 62 is caused to be moved along the
pin 61, under the urging of the spring 43 to cause the
~lange 67 of the eyelet to engage the ground plate 86, and
establish a shortened current path.
Another embodiment 120 of this invention includes
provisions made for direct test access to the tip and ring
line conductors of the protector assemblies. Referring
more to FIGS. 18-21, it is seen that a housing 121 is
provided with two access openings 122-122 adjacent to the
handle portion 38. The protector assembly 120 includes two
current protection subassemblies 41-41', two voltage
protection subassemblies 42-42~, a grounding
subassembly 44, and two springs 43-43.
~ dditionally, the protector assembly 120 includes
two spring retainers 126-12~ (see also FIGS. 22-23). The
spring retainer 126 is cup-shaped and has an eccentrically
disposed portion 127 and is made of a metallic material~
In an inner end of each retainer is disposed a spring 43.
The embodiment also includes an insulator 131
(see FIG. 24j which is made of a plastic material and which
~zn~ 0
-- 19 --
includes a flange 132. T~le insulator 131 extends into the
spring ~3 with the flange 132 prevent:ing its spring from
touching the cup 93.
A wire strap 141 (see FIGS. 25-27) is provided to
extend each circuit electrically to the vicinity of the
access openings 122-122. The strap 141 includes a hooked
end portion 142~ a portion 143, which is covered with an
insulative material 144 and an end portion 146. The
strap 141 is adapted to be received in the eccentric
portion 127 of the spring retainer 126 with the end
portion 146 also enyaging the outer diameter face of the
compression spring 43. A flattened or swaged portion 147
of the hooked end of the strap 141 extends between the
exposed face of the center electrode 101 and the flange 56
of the eyelet 62.
The wire strap 141 is assembled with the modified
housing 121, the current protector subassembly 41, the
voltage protection subassembly 42, and the ground
assembly 44. Insulation is used to cover the portion 143
inasmuch as it extends adjacent to the cup 93. But for the
insulation, inadvertent undesired electrical engagement
between the cup 93 and the wire strap could occur.
The need for the insulator 131 becomes apparent
from a study of the detail assembly of the embodiment 120
which is shown in FIGS~ 19-20. One end of the spring 43 is
received in, and engages the inner portion of, the cup-
shaped retainer 125. The end of the strap 141 is in
electrical contact with the retainer 126 and the spring 43
In the embodiment 30 shown in FIGo 3, the spring 43 is
electrically connected to the cup 93, and so is at ground
potential; however, the cup and the spring are disposed
within an insulated housing 32. On the other hand, in the
embodiment 120, the strap 141 completes a circuit from the
line pin 61 to the spring 43. If the spring 43 were not
insulated from the cup 93, which is grounded, ~he normal
~urrent path would be shorted to ground. The insulator 131
removes the spring from its normally idle ground circui-t
~2~
- 20 -
and accommodates it as an idle component in the normal
current circuit.
It should be understood that while the preferred
embodiment of this invention includes two identical
protector assemblies disposed within a single housing, the
invention is not so limited. For example, the heat coil
and/or voltage protection characteristics on one side need
not be identical to those on the other side. The voltage
protection can be changed by changing the gap 99, and the
current protection can be changed by providing more or less
resistance in the wound wire.
Further, the present invention is not limited to
protector units in which the sleeves of the heat coil
assemblies are fusibly bonded to the line pin3 as in the
preferred embodiment described hereinabove. Each heat coil
subassembly could include a sleeve fusibly bonded to a
separate pin which is mounted on an individual half-base.
